Thanks to the massive success of The Hangover, director Todd Phillips officially took back the belt from Judd Apatow as the go-to guy for R-rated man-child comedy. Due Date sees Phillips team up with Hangover star Zach Galifianakis a second time, but fans should be warned against expecting similar results. Robert Downey Jr. stars as Peter, a tightly wound expectant father forced into an unlikely cross-country road trip with aspiring actor Ethan (Galifianakis) and his French bulldog in order to make it home in time for his child’s birth. The film has some standout moments, but unfortunately they’re not strung together well enough for Due Date to live up to the inevitable comparisons.

Know this up front: Due Date is not as funny as The Hangover. Sure, it’s got Phillips reuniting with his new muse, Galifianakis, another family event as a ticking deadline, and a laundry list of appropriately absurd situations, but somewhere along the way this road-trip comedy takes a wrong turn.

Given the promising pairing of Downey, Galifianakis and Phillips, you keep waiting for Due Date to hits its stride, but both the tone and jokes go through uncomfortable ups and downs; the movie goes from gross-out to sad faster than Peter loses his cool. Phillips is a stronger director than you’d expect from the number of masturbation jokes in his movies, and Due Date both looks and sounds great. Unfortunately, the script-by-committee isn’t similarly polished, so when the movie gets out of control, it’s not always a good thing. Where The Hangover was a comedy ingeniously structured like a detective story, Due Date uses the familiar road trip format to move its odd couple between misadventures. And while the specific events are just as unpredictable, the result isn’t nearly as inventive or fun.

Much like instant guy classic The Hangover, Due Date is extremely male-centric. Apart from a few minutes of a pregnant Michelle Monaghan here and a Juliette Lewis cameo there, this is an otherwise male-dominated cast. Once again, that means male bonding and over-the-top high jinks, but Due Date is more transparent about its serious side. With Ethan having recently lost his father, and Peter about to become one (whether or not he’s there for it), Due Date is heavily concerned with fatherhood and what it means to be a mature, responsible adult. It’s a fine line to walk for a notoriously immature director, but Galifianakis and Downey’s unique chemistry helps enormously. Still, the metered doses of sentimentality don’t always jive with the film’s mean-spirited moments (some of the more shockingly funny in recent memory). If the laughs came at a more rapid-fire pace, chances are you wouldn’t even notice. Ultimately though, Due Date just isn’t consistently funny enough to distract from its flaws.